docs: def one_phase_dP_gravitational(angle, rho, L=1.0, g=g):
      r'''This function handles calculation of one-phase liquid-gas pressure drop
      due to gravitation for flow inside channels. This is either a differential 
      calculation for a segment with an infinitesimal difference in elevation (if
      `L`=1 or a discrete calculation.
      
      .. math::
          -\left(\frac{dP}{dz} \right)_{grav} =  \rho g \sin \theta
      
      .. math::
          -\left(\Delta P \right)_{grav} =  L \rho g \sin \theta
      
      Parameters
      ----------
      angle : float
          The angle of the pipe with respect to the horizontal, [degrees]
      rho : float
          Fluid density, [kg/m^3]
      L : float, optional
          Length of pipe, [m]
      g : float, optional
          Acceleration due to gravity, [m/s^2]
  
      Returns
      -------
      dP : float
          Gravitational component of pressure drop for one-phase flow, [Pa/m] or
          [Pa]
          
      Notes
      -----
          
      Examples
      --------    
      >>> one_phase_dP_gravitational(angle=90, rho=2.6)
      25.49729
      >>> one_phase_dP_gravitational(angle=90, rho=2.6, L=4)
      101.98916
      '''
      angle = radians(angle)
      return L*g*sin(angle)*rho